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Author Topic: KM84i Internal Impedance Jumpers  (Read 3066 times)

headstack

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KM84i Internal Impedance Jumpers
« on: June 02, 2014, 11:23:22 PM »

Was wondering what the procedure is for switching the KMi from 50 ohms to 200 ohms.

It appears that the two outer jumpers are removed, and one is placed in the center 200 ohm position.

Is this correct?

Thank you
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klaus

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Re: KM84i Internal Impedance Jumpers
« Reply #1 on: June 03, 2014, 11:17:31 AM »

Correct.
Also make sure that the two 56Ω pad resistors are bridged.

See David Satz's excellent primer on the subject here:
http://repforums.prosoundweb.com/index.php/topic,1421.msg7812.html#msg7812

And don't forget the mandatory insertion of your REAL name into your posts and profile!

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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

mike_mccue

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Re: KM84i Internal Impedance Jumpers
« Reply #2 on: June 05, 2014, 01:47:41 PM »

Hi Klaus,
 You have recently pointed me to David Satz's posts and that is when I learned about the 56k resistors.

 Is there a convenient photo of them somewhere on the web. I am thinking about asking a friend of mine who owns a couple of KM84s, that he understands to be wired as 50ohm output, if he wants to take a look at what is inside his mics.

 Thanks.
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Mike McCue
Tallahassee Florida USA

klaus

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Re: KM84i Internal Impedance Jumpers
« Reply #3 on: June 05, 2014, 02:30:11 PM »

If you enlarge the top picture of four KM88 on this page:
http://recordinghacks.com/microphones/Neumann/KM-88
you will see the two 56Ω resistors, directly below the transformer in the picture. Though this is a shot of a KM88, the arrangement of the resistors is identical in KM84.

Before you have your friend remove the resistors: Often they are already bridged with a solder bridge (test with ohm meter!), so they can stay there. And if they need to be removed to bridge the solder traces below them, tell you friend to use a solder iron with a very fine point: the inner resistor is very close to the transformer, and the transformer bobbin can melt if too much heat is generated.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

mike_mccue

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Re: KM84i Internal Impedance Jumpers
« Reply #4 on: June 05, 2014, 02:37:00 PM »

Thanks Klaus!
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Mike McCue
Tallahassee Florida USA
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